Guys,
Do you use/trust CNC tape to hold your cut piece to the spoilboard? Or do you fasten your parts down?
I’ve seen CNC tape used a lot on youtube videos with uses ranging from timber to aluminium.
It would be really nice to think it would work. Not sure id feel safe milling aluminium parts and have them only held by tape. I picture the parts losing grip and flying at me. Maybe a good horror movie plot.
Ta
I have used blue painters tape/super glue, and it works fine, however, I have had better luck with “carpet tape”. It is essentially doubled sided tape, however it kind of has a mesh pattern to it, and it is 2-3x thicker than normal tape. For me this was nice because I am often milling rough hardwood lumber, and it is not always perfectly flat, so the super glue/painters tape doesn’t work.
The benefit of double stick tape is that you can get to all sides and the top of your workpiece without interference. I have never had a workpiece come off the spoil board while milling, granted sometimes I probably put on more tape than needed 
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I haven’t tried it yet on my Primo but we’ve used it at work with pretty good success. I think surface area is a big factor.
I have seen a few people on the forum have success using the superglue trick that @PKochZ71 describes above.
This for example.
Although this constgitutes the weakest kind of “proof”
I used double sided carpet tape successfully to mill LR4 XZ plates.
The “I did it and it worked” is a weak proof, because it does not take into account other variables. Would it have worked on smaller pieces? Or with different spoilboard material? Or even the same material in different condition? I can’t say. My MDF spoilboard wasw fairly new then. OIt has many grooves in it NOW because I have used it as … well, a spoilboard by cutting into ti several times with different patterns at different depths. Those grooves reduce the available surface area for the tape, and may bring more dust into play. They also make for weak islands which might shear off from the main spoilboard.
So… the answer is “maybe.” we still have only some theoretical numbers on cutting loads, and about the only thing we’ve proved is that the LR4 is more capable than the LR3 was. How much load can x square mm of double sided tape restrain? We don’t know that either, but I can say that 2 strips of carpet tape on reasonably fresh MDF holding to the peel-off layer on an alumimium sheet held with seemingly lots to spare for a piece the size of a LR4 XZ plate.
Cool, thanks, i guess your weak proof is my proof of concept 
Once my workpiece is set down with tape, I always give it a very firm side to side push by hand just to ensure it feels secure. Would rather it come off by hand than via the tool in the middle of a cut job.
I used this method when cutting the aluminum XZ plates for my LR4 as well. Taped one side of the aluminum with blue painters tape, did the same to a scrap piece of melamine, then used an adhesive “Gorilla Glue” spray (I suspect something like wood glue would work as well) and glued the two taped sides together. Screwed the piece of melamine down to my spoilboard and it held the aluminum incredibly well (it was actually a little tricky prying them apart, but you just need to use a chisel or something to get in between the aluminum and melamine). Then you peel off the leftover painters tape and ta-da!
I am using clamps more and more, blue tape seems to have gotten expensive!
I used double sided tape on most tings, but over 1/2” and thicker, I use that and a screw or two just in case
This is what I get off amazon. Works great
I also use Brad nails - they leave only a small hole compared to screws.
I have a brad nailer, and tried it a few times… the brad nails that I have are really difficult to pull out. A few have broken off rather than come out and practically all of them pulled the head through the work piece.
So I just bought more tape…
That could be a feature rather than a bug. If you can place the brads where the pull-through hole isn’t a blemish on the finished work piece then there should be enough brad sticking out to grab it with some pliers or a vice grip.
Lots of nails for use in nail guns are coated with a glue that gets heated up by the friction of the nail going through the wood, which then improves the holding power. Maybe look for a brand with little or no glue coating for this particular use case.
Yeah that’s what I do
It just occurred to me that a pin nailer might work here too, as long as there weren’t significant lifting forces on the workpiece.
Be careful with the pin nailer. It is strong laterally but can pull up vertically very easily especially with an mdf spoil board.
I was excited about these plastic nail guns until I realized that they are more expensive than my use case warrants. https://raptornails.com/
But this thread is great, I grabbed some “CNC tape” to try out! Usually I use pocket hole screws and wooden clamps directly into the spoilboard, but that’s not always ideal.
I still think that it is safer to securely fix the workpiece on the workbench using fixtures or other appropriate clamping devices.
Apparently you can use a conventional nailer, with a few caveats (see my conversation with the manufacturer in the linked thread)
I use blue tape and ca glue ALOT! It works great. If you use it on entire piece holding tabs are not necessary!. My piece will not bow from too much pressure, etc! I would not condemn double sided tape until you try it. Used it just the other day for my aluminum plates on my lr4. Much more hold there then one would think!